Gene therapy may improve incurable form of blindness

Scientists at the University of Oxford in the UK have restored some sight in people who have a degenerative eye disease by replacing a defective gene in their retinas with a working version of the same gene.

The people who received the procedure - which is delivered using a single injection - have an inherited type of genetic blindness called choroideremia, which is caused by a mutation in the CHM gene.

Choroideremia affects about 1 in 50,000, and people who have this condition get progressively worse vision, eventually becoming completely blind around middle age.

Blindness in people with choroideremia is caused by the degenration of the rods and cones (or "photoreceptors") in the eye's retina that send visual information to the brain, and there is no treatment available to correct this.

As part of the first phase of a clinical trial, six male patients aged between 35 and 63 with choroideremia were injected with a genetically engineered, harmless virus (called a "vector") containing a normal, healthy copy of the CHM gene.

The researchers hoped that this functioning gene would stop the cells in the patients' photoreceptors from dying. The patients in the study were not blind, but the choroideremia was more advanced in some patients than in others.

What happened?

Six months after the injections, the team conducting the trial found the retinas in all of the patients had improved sensitivity to light and that two patients had substantially improved vision.

These two patients had the most advanced form of choroideremia, and after they received the treatment they were able to correctly read an extra two and four lines on an eye chart, respectively. No adverse effects from the injection were recorded in the trial.

These results, which have been published in The Lancet medical journal, are encouraging, though this is just the first phase of a trial with a small sample group. So far the researchers have analyzed only the data from the first 6 months after the procedure, so we do not know what the long-term effects of this kind of treatment are.

Writing on the results of the trial, Hendrik Scholl from John Hopkins University in Baltimore, MD, and José Sahel from the Institut de la Vision in Paris, France said:

"The short follow-up of the new study prevents any conclusion about preventing degeneration in the long term. It remains to be determined if gene therapy will have an effect on the progression of photoreceptor degeneration. Even if the effect turns out to be only slight, this might have important positive implications because there are additional therapeutic avenues targeting photoreceptors that could help to save or restore visual function."

This is the first study to look at the effects of this kind of gene therapy in people who have a genetic problem with the photoreceptors of the eye. The researchers think that the results of their study so far show potential for gene therapy to be used not just to treat choroideremia, but also other, more common degenerative eye diseases, such as age-related macular degeneration.

The Tommy Salisbury Choroideremia Fund

The research was funded through the charity Fight for Sight and the Tommy Salisbury Choroideremia Fund. Tommy Salisbury is a 13-year-old boy from Kent in the UK, who was diagnosed with choroideremia aged 5. In 2005, his parents established the Tommy Salisbury Choroideremia Fund, which has so far raised nearly $600,000 for researching potential treatments.

Professor Robert E Maclean, who led the research, had this to say about the Tommy Salisbury Choroideremia Fund's contribution to his work:

"In my opinion, this is the single most significant factor that has enabled us to lead the world in starting the first clinical trial for this disease. We shouldn't underestimate the power that individuals can have in influencing the course of research through their fundraising activities."

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